Menuconfig transport selection does not propagate to vendored libmicroros build

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### Summary

Selecting `Micro XRCE-DDS over UART` under `micro-ROS Settings > micro-ROS network interface select` in `idf.py menuconfig` sets the ESP-IDF-side transport wrapper but has no effect on the vendored colcon build that produces `libmicroros.a`. The rmw layer is still compiled with `-DRMW_UXRCE_TRANSPORT=udp` from the vendored `colcon.meta`, so `RMW_UXRCE_TRANSPORT_CUSTOM` is never defined, `rmw_microros/rmw_microros.h` skips the guarded include of `custom_transport.h`, and any call to `rmw_uros_set_custom_transport()` fails at compile time with `-Werror=implicit-function-declaration`.

A workaround exists via `app-colcon.meta` at the app root, the pickup is already implemented in `CMakeLists.txt` and threaded through `libmicroros.mk` as `APP_COLCON_META`.

### Environment

- Branch: `jazzy`
- Commit: `16cf0d534e618c2752e5546710cd2c81c0a586cc`
- Target: ESP32-S3 DevKitC-1
- ESP-IDF: v5.3.5
- Host: Ubuntu 24.04 on WSL2

### Reproducer

```bash
# From an ESP-IDF project with this component vendored under components/
idf.py set-target esp32s3
idf.py menuconfig
# Component config -> micro-ROS Settings -> micro-ROS network interface select -> "Micro XRCE-DDS over UART"
idf.py clean-microros
idf.py build
```

Application code calling `rmw_uros_set_custom_transport()` fails:

```
error: implicit declaration of function 'rmw_uros_set_custom_transport'
[-Werror=implicit-function-declaration]
```

The generated `rmw_microxrcedds_c/config.h` confirms the root cause:
```
#define RMW_UXRCE_TRANSPORT_UDP
/* #undef RMW_UXRCE_TRANSPORT_CUSTOM */
```

The menuconfig transport symbol `CONFIG_MICRO_ROS_ESP_UART_TRANSPORT=y` never enters the colcon build; the vendored `colcon.meta` hard-codes `-DRMW_UXRCE_TRANSPORT=udp` and this wins by default.

### Verified workaround

Create `app-colcon.meta` at the app root (sibling to `main/`), using the required `"names"` wrapper:
```json
{
"names": {
"rmw_microxrcedds": {
"cmake-args": [
"-DRMW_UXRCE_TRANSPORT=custom"
]
}
}
}
```

Then `idf.py clean-microros && idf.py build`. Verified end to end on the environment above: `RMW_UXRCE_TRANSPORT_CUSTOM` is defined in the built `config.h` and the application compiles and links cleanly.

Note: the "names" wrapper is required. A JSON body without it is parsed successfully, added to --metas, and its contents silently ignored, reproducing the original compile error with no signal that the override was rejected.

### Proposed fix

Have the component's `CMakeLists.txt` map the Kconfig transport selection to the correct `RMW_UXRCE_TRANSPORT` value and generate a small meta file in the build tree, passed to colcon via the existing `APP_COLCON_META` seam. Any user-supplied `app-colcon.meta` continues to override the generated one, so nothing that already works breaks.

On the jazzy branch, `Kconfig.projbuild` exposes exactly three network-interface options, so the mapping is minimal:

- `CONFIG_MICRO_ROS_ESP_NETIF_WLAN` -> `udp`
- `CONFIG_MICRO_ROS_ESP_NETIF_ENET` -> `udp`
- `CONFIG_MICRO_ROS_ESP_UART_TRANSPORT` -> `custom`

Sketch (approve-or-steer level, not the final diff):

```cmake
if(CONFIG_MICRO_ROS_ESP_UART_TRANSPORT)
set(UROS_RMW_TRANSPORT "custom")
elseif(CONFIG_MICRO_ROS_ESP_NETIF_WLAN OR CONFIG_MICRO_ROS_ESP_NETIF_ENET)
set(UROS_RMW_TRANSPORT "udp")
else()
set(UROS_RMW_TRANSPORT "udp")
endif()

set(UROS_KCONFIG_META "${CMAKE_BINARY_DIR}/uros_kconfig_transport.meta")
file(WRITE ${UROS_KCONFIG_META}
"{\"names\": {\"rmw_microxrcedds\": {\"cmake-args\": [\"-DRMW_UXRCE_TRANSPORT=${UROS_RMW_TRANSPORT}\"]}}}\n"
)

# Compose APP_COLCON_META so user-supplied app-colcon.meta still wins
set(UROS_APP_COLCON_META "${UROS_KCONFIG_META}")
if(EXISTS "${PROJECT_DIR}/app-colcon.meta")
set(UROS_APP_COLCON_META
"${UROS_KCONFIG_META} ${PROJECT_DIR}/app-colcon.meta")
endif()
```

Users on WLAN or Ethernet: unchanged (both resolve to `udp`, matching the current vendored `colcon.meta`). Users with an existing `app-colcon.meta`: unchanged (their file is passed last and still wins). Users who edited the vendored `colcon.meta` directly: still works (their edit is the first `--metas` entry; the generated meta comes after and overrides only the transport field).

### Cache invalidation

One rough edge worth flagging: changing the menuconfig transport option changes the content of the generated meta, but colcon's build cache for `libmicroros.a` is not invalidated on that change. An initial PR would preserve that behaviour and add a README note that `idf.py clean-microros` is required after any transport change. A follow-up PR could make the generated meta a proper build dependency of `libmicroros.a` for automatic invalidation; I would prefer to keep those separate.

### Ask

I would like to submit this fix. Before writing the PR I want to confirm two things:

1. Is auto-generating the transport meta from Kconfig the direction you want? If you prefer a smaller change (README-only clarification of the `app-colcon.meta` workaround, its `names` schema requirement, and its silent-failure trap) I am happy to do that instead.
2. Is `${PROJECT_DIR}/app-colcon.meta` the correct convention for the "app root" pickup on jazzy? That matches the existing `CMakeLists.txt` lines around 26-28; I want to confirm this generalises before I compose against it.

Diagnosis and workaround verified with ESP-IDF v5.3.5. Happy to attach a minimal reproducer as an example under `examples/` if useful.

Thanks for maintaining this component.

Bắt đầu với các tùy chọn transport trong Kconfig.projbuild và cách xử lý APP_COLCON_META hiện có trong CMakeLists.txt quanh các dòng 26-28, sau đó theo dõi cách libmicroros.mk truyền metadata vào bản build colcon vendored. Tái hiện cấu hình UART bằng các lệnh idf.py được liệt kê và kiểm tra rmw_microxrcedds/config.h được tạo ra. Công việc được xem là hoàn tất khi transport được chọn đi đến cấu hình được tạo ra và ứng dụng build thành công với bước clean được ghi lại trong tài liệu.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.